Permanent magnet synchronous machines (PMSM) are getting increasingly more popular due to their high torque and power density. The main drawbacks are the magnet price, the difficulties with field weakening, and possibly the assembly/disassembly that is somewhat difficult due to high forces emanating from the magnets.
Another problem is that the metals used in alloys for producing permanent magnets are a restricted nature resource, and from a global environmental point of view there is a requirement for less use of such metals, as there is no endless source thereof.
Electrically magnetized synchronous machines (EMSM) have almost the same properties as permanent magnet synchronous machines. However, one drawback thereof is the need for a field winding in the rotor, and a corresponding power supply and slip rings or rotary transformer plus rectifier to deal with the magnetization. An advantage using electrically magnetized synchronous machines compared to permanent magnet synchronous machines is the ease of carrying out field weakening.